U.S. patent number 6,026,821 [Application Number 09/192,705] was granted by the patent office on 2000-02-22 for method of and hair dryer for drying hair using remote sensing of the moisture content of the hair.
This patent grant is currently assigned to U.S. Phillips Corporation. Invention is credited to Frits Last.
United States Patent |
6,026,821 |
Last |
February 22, 2000 |
Method of and hair dryer for drying hair using remote sensing of
the moisture content of the hair
Abstract
Hair dryer with remote sensing of the moistness of the hair by
means of a detector which compares the amount of radiant energy in
two absorption bands in the spectrum of light emitted by an infra
red source and reflected by the hair. One of the absorption bands
is caused by water in the hair. The amount of radiant energy in
this absorption band changes significantly during the drying of the
hair. The other absorption band is caused by keratin in the hair.
The energy in this band changes to a much smaller extent during the
drying of the hair. The intensity ratio of the two bands is an
indicator for the moistness of the hair and can be employed to
control the temperature and/or the air flow of the hair dryer.
Inventors: |
Last; Frits (Drachten,
NL) |
Assignee: |
U.S. Phillips Corporation (New
York, NY)
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Family
ID: |
8228953 |
Appl.
No.: |
09/192,705 |
Filed: |
November 16, 1998 |
Foreign Application Priority Data
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Nov 21, 1997 [EP] |
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97203646 |
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Current U.S.
Class: |
132/200; 132/206;
132/211 |
Current CPC
Class: |
A45D
20/12 (20130101) |
Current International
Class: |
A45D
20/12 (20060101); A45D 20/00 (20060101); A45D
024/00 (); A45D 007/06 (); A45D 007/02 () |
Field of
Search: |
;132/200,206,211 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0679350A1 |
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Nov 1995 |
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EP |
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3433246C2 |
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Mar 1986 |
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DE |
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97/09898 |
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Mar 1997 |
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WO |
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Primary Examiner: Wilson; John J.
Assistant Examiner: Doan; Robyn K.
Attorney, Agent or Firm: Bartlett; Ernestine C.
Claims
I claim:
1. Method of drying hair by supplying hot air, using remote sensing
of the moisture content of the hair, wherein amounts of radiation
energy in at least one absorption band of radiation reflected from
the hair are measured, the at least one absorption band being
caused by the moisture content of the hair and the change of the
amount of radiation energy in the at least one absorption band
being used as a measure of the change of the amount of the moisture
content, and the stream of hot air is controlled in response to the
change.
2. A method of drying hair by supplying hot air, using remote
sensing of the moisture content of the hair, wherein amounts of
radiation energy in at least two absorption bands of radiation
reflected from the hair are compared with one another, one of the
absorption bands being caused by moisture in the hair and another
one of the absorption bands being caused by a moisture-independent
characteristic of the hair, the ratio between the amounts of
radiation energy in the at least two absorption bands being used as
a measure of the moisture content, the stream of hot air being
controlled in response to the ratio.
3. A method as claimed in claim 2, wherein the other one of the
absorption bands is caused by keratin in the hair.
4. A method as claimed in claim 2, wherein the one absorption band
is situated around 1420 nm and the other absorption band is
situated around 2058 nm.
5. A method as claimed in claim 2, wherein the hair is irradiated
by means of an infrared light source whose intensity is
modulated.
6. A method as claimed in claim 2, wherein the radiation reflected
from the hair is focused onto a grating by means of a lens and the
amounts of radiation energy are measured by means of sensors
arranged at that side of the grating which is remote from the
lens.
7. A hair dryer including means for supplying a stream of hot air
for drying moist hair and means for the remote sensing of the
moisture content of the hair, wherein the hair dryer comprises:
means for measuring amounts of radiation energy in at least one
absorption band of radiation reflected from the hair, the at least
one absorption band being caused by the moisture content of the
hair, means for determining the change of the amount of radiation
energy in the at least one absorption band, the chance of the
amount of radiation energy in the at least one absorotion band
being used as a measure of the change of the amount of the moisture
content, and means for controlling the stream of hot air in
response to the change.
8. A hair dryer including means for supplying a stream of hot air
for drying moist hair and means for the remote sensing of the
moisture content of the hair, wherein the hair dryer comprises:
means for measuring amounts of radiation energy in at least two
absorption bands of radiation reflected from the hair, one of the
absorption bands being caused by moisture in the hair and another
one of the absorption bands being caused by a moisture-independent
characteristic of the hair, means for determining the ratio between
the amounts of radiation energy in the at least two absorption
bands, and means for controlling the stream of hot air in response
to the ratio.
9. A hair dryer as claimed in claim 8, wherein the other one of the
absorption bands is caused by keratin in the hair.
10. A hair dryer as claimed in claim 8, wherein the one absorption
band is situated around 1420 nm and the other absorption band is
situated around 2058 nm.
11. A hair dryer as claimed in claim 8, wherein the hair dryer
includes an infrared light source for irradiating the hair, and
means for modulating the intensity of the light source.
12. A hair dryer as claimed in claim 8, wherein the hair dryer
further includes: a grating, a lens for focussing the radiation
reflected from the hair onto the grating, and sensors, arranged at
that side of the grating which is remote from the lens, for
measuring the amounts of radiation energy.
Description
BACKGROUND OF THE INVENTION
The invention relates to a method of drying hair by supplying hot
air, using remote sensing of the moisture content of the hair.
The invention also relates to a hair dryer including means for
supplying a stream of hot air for drying moist hair and means for
the remote sensing of the moisture content of the hair.
Such a method and hair dryer are known from Patentschrift DE 34 33
246. During hair drying there is always a risk that the hair is
made too dry by the hot air from the hair dryer, as a result of
which the hair is liable to be damaged. The temperature increases
rapidly where the hair has dried, which is detrimental to the hair
and painful for the scalp. For a satisfactory and comfortable
result it is therefore important to know how much moisture is left
in the hair and to take steps if the moisture content decreases
below a given limit. In the known hair dryer the moisture content
is measured by means of a moisture sensor disposed in the
circulating air stream in a hair-drying hood. The measurement of
the moisture content of the hair is then measured remote from the
hair but is limited to hair-drying hoods in which the hot air
circulates. However, this known method of moisture measurement
cannot be used in the case of hand-held hair-dryers because in
these dryers no hot air circulates within an enclosed space.
Furthermore, hair dryers are known, for example from International
Application WO 97/09898, which have electrodes arranged on an
accessory which comes into contact with the hair during drying. By
means of the electrodes the moistness of the hair is measured on
the basis of the resistance or capacitance of the hair between the
electrodes. However, in this type of dryer the measurement of the
moistness of the hair is not effected at a distance and has
therefore only a limited field of use.
From the Demande de brevet europeen EP 0 679 350 a hair dryer is
known in which the temperature of the hair to be dried is measured
in a contactless manner, at a distance from the hair, by means of
an infrared sensor arranged on the housing of the hair dryer. The
temperature of the hair is then determined on the basis of the
infrared radiation emitted by the hair. However, the temperature of
the hair is only an indirect indication of the moisture content of
the hair and is consequently less reliable.
SUMMARY OF THE INVENTION
Therefore, there is a need for hair dryers and methods of drying
moist hair using remote sensing of the moisture content of the
hair. To this end, according to the present invention, the method
of the type defined in the introductory part is characterized in
that amounts of radiation energy in at least one absorption band of
radiation reflected from the hair are measured, the at least one
absorption band being caused by moisture in the hair and the change
of the amount of radiation energy in the at least one absorption
band being used as a measure of the moisture content, and the
stream of hot air is controlled in response to the change. The hair
dryer includes means for supplying a stream of hot air for drying
moist hair and means for the remote sensing of the moisture content
of the hair and it dryer comprises: means for measuring amounts of
radiation energy in at least one absorption band of radiation
reflected from the hair, the at least one absorption band being
caused by moisture in the hair, means for determining the change of
the amount of radiation energy in the at least one absorption band,
and means for controlling the stream of hot air in response to the
change.
The amount of moisture in the hair is determined in that the amount
of radiation in an absorption band specific to water is measured
during the drying process. The amount of radiation in said
absorption band reflected from the hair changes as the hair becomes
dryer. By measuring the radiation at given intervals it is possible
to predict when the hair will be dry.
A more accurate measurement result is obtained by a variant of the
method which is characterized in that amounts of radiation energy
in at least two absorption bands of radiation reflected from the
hair are compared with one another, one of the absorption bands
being caused by moisture in the hair and another one of the
absorption bands being caused by a moisture-independent
characteristic of the hair, the ratio between the amounts of
radiation energy in the at least two absorption bands being used as
a measure of the moisture content, and the stream of hot air is
controlled in response to the ratio. The corresponding variant of
the hair dryer is characterized in that the hair dryer comprises:
means for measuring amounts of radiation energy in at least two
absorption bands of radiation reflected from the hair, one of the
absorption bands being caused by moisture in the hair and another
one of the absorption bands being caused by a moisture-independent
characteristic of the hair, means for determining the ratio between
the amounts of radiation energy in the at least two absorption
bands, and means for controlling the stream of hot air in response
to the ratio.
The amount of moisture in the hair is now determined by comparing
the absorption bands of water with a fixed reference band,
preferably the absorption band of keratin. Keratin is a
water-insoluble substance forming the principal constituent of the
hair. During hair drying the reflection of the hair changes as a
result of the decreasing amount of water, while the reflection of
the keratin in the hair remains constant because the amount of
keratin remains constant. The absolute value of the reflection as a
result of water is, in itself, not always a reliable measure of the
amount of water in the hair because the absolute value also depends
on the distance between the hair and the sensor by means of which
the amount of radiation is measured and on the intensity and the
spectrum of the radiation source which emits the radiation to the
hair. The absolute value of the reflection by the keratin depends
on the distance and on the radiation source in a similar manner.
Since the amount of keratin does not change during the drying
process the ratio between the amounts of radiation in an absorption
band of water and an absorption band of keratin is a good measure
of the moisture content of the hair. By means of the measured
moisture content the temperature and/or the strength of the air
stream can be controlled so as to obtain an optimum result.
Water and keratin each have characteristic absorption bands in the
spectrum of the reflected radiation. The absorption bands should
not overlap one another and preferably lie in a spectral range
which can be measured by means of one conventional type of sensor.
The water absorption band around 1420 nm and the keratin absorption
band around 2058 nm are suited and lie within the near infrared
region which can be detected by means of PbS photoconductive
sensors.
The hair is preferably irradiated by means of an infrared light
source having optical focusing means arranged on the hair dryer.
However, other light sources, which happen to be present or which
have been installed intentionally for this purpose in the proximity
of the hair to be dried can also be used provided that they emit
energy in the relevant absorption bands. A suitable light source is
an infrared halogen lamp having a continuous spectrum or a system
of light sources having a narrow spectrum and a high spectral
emission in the absorption bands to be measured.
By modulating the intensity of the light source, for example by
chopping the light by means of a rotating filter wheel in the light
path of the light source, it is possible, at the detection side, to
make a distinction between reflection as a result of undesired
background radiation and reflection as a result of the light
source.
In order to enable the amount of radiation energy in the at least
two different absorption bands to be measured, spectral selection
is required. For this purpose, the reflected radiation can be
focused onto a diffraction grating by means of a lens system, which
grating diffracts the spectrum of the radiation in dependence upon
the wavelength. The grating is followed by sensors arranged at
suitably selected positions corresponding to the absorption bands
to be measured.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the invention will be described and
elucidated with reference to the accompanying drawings, in
which
FIG. 1 represents the spectral reflection in the near-infrared
spectrum for hair with a varying degree of moistness;
FIG. 2 shows a hair dryer with moistness sensing in accordance with
the invention;
FIG. 3 is an electrical block diagram of a hair dryer in accordance
with the invention; and
FIG. 4 shows a measurement system for remote sensing of the
moistness of hair.
In the Figures parts or elements having a like function or purpose
bear the same reference symbols.
By utilizing the effect that water absorbs given wavelengths in the
near-infrared radiation region to a greater extent than other
wavelengths, it is possible to make a statement about the degree of
moistness of the hair of the head. The absorption depends inter
alia on the thickness of the layer of water on the hair. More
infrared radiation will be absorbed as the layer of water increases
in thickness. By irradiating the moist hair with infrared light the
changing absorption in the spectrum reflected from the hair being
dried can be measured by means of a sensor. The hair drying process
can be controlled on the basis of such a measurement.
However, the problem may then be encountered that the absolute
value of the reflected light energy depends not only on the amount
of water in the hair but also on the distance between the sensor
and the hair and on the amount of light from the light source. This
problem can be solved by also measuring the reflection from a
substance which is characteristic of the hair and whose composition
and quantity does not change during drying of the hair. The
reflection from said substance then functions as a reference. The
principal constituent of hair is a water-insoluble protein called
keratin. The absorption of the infrared radiation by keratin
changes hardly during the drying process. Comparing the intensities
of absorption bands of water with those of keratin yields a
characteristic value which is a measure of the moistness of the
hair. The spectrum reflected from water exhibits absorption bands
in the near-infrared region around 935 nm, 1420 nm and 1930 nm. The
spectrum reflected from keratin exhibits absorption bands around
1495 nm, 1690 nm, 1733 nm and 2058 nm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 represents the reflection r from dark blond hair as a
function of the wavelength w between 400 and 2400 nm. Curve a
relates to moist hair, the intermediate curves b, c, d and e relate
to decreasingly moist hair, and curve f relates to dry hair. At
1420 nm there is a distinct dip as a result of water in the hair.
This dip becomes smaller as the hair becomes drier. At 1930 nm a
second dip is visible, also as a result of water in the hair. At
2058 nm a dip is visible, which is the result of absorption by
keratin. Measuring the amount of radiation energy around one of the
dips as a result of water, for example at 1420 nm, by means of a
first sensor, measuring the radiation energy around one of the dips
as a result of keratin, for example at 2058 nm, by means of a
second sensor, and dividing the measurement results by one another,
now yields a ratio which is a measure of the moisture content of
the hair. Other types of hair, such as black hair or grey hair,
yield curves having a different shape but having dips at the same
positions in the reflected spectrum.
The desired absorption bands must be selected from the reflected
spectrum. This can be effected, for example, by means of a
diffraction grating having a grating constant of 4 micrometers, on
which the reflected infrared light is focussed. The grating is
followed by the sensors arranged at positions which correspond to
the spectral bands to be measured. The hair is illuminated by means
of an infrared light source having focussing means, for example a
50 W tungsten halogen lamp having a filament temperature of 2269 K,
but any other light source with spectral emission in the absorption
bands to be measured is suitable for this purpose.
In order to enable a distinction to be made between undesired
background radiation and the desired radiation resulting from
irradiation of the hair by means of the infrared light source,
preferably the intensity of the light source is modulated, for
example by chopping the light by means of a rotating filter wheel
which is driven by an electric motor. In practice, a chopping
frequency of 600 Hz appears to be satisfactory. The reflected
radiation then contains a static component, as a result from the
background radiation, and a modulated component, as a result of
chopping of the light source. In the received sensor signal the
modulated signal component can be isolated from the static
component by means of a band-pass filter and can subsequently be
processed. Instead of chopping it is also possible to turn on and
turn off the light source itself if the properties of the light
source allow this or make this possible.
The sensors by means of which the reflected radiation is measured
should be sensitive in the near-infrared region and should deliver
an adequate signal. Photoconductive sensors using lead sulphide
(PbS) are suitable for this purpose.
FIG. 2 shows a hair dryer which features moistness measurement
using the principle described hereinbefore. The hair dryer has a
housing 2 having a grip 4 on which an actuating switch 6 is
situated. The housing accommodates (not shown) a heating element, a
fan and electronic control devices with associated power supply.
The air drawn in by the fan and heated by the heating element
leaves the housing at an outlet opening 8 and heats the hair 10 to
be dried. At a suitably selected location the housing 2 carries an
infrared light source 12 and a detector 14. The light source 12
projects infrared light onto the hair 10. The light reflected from
the hair 10 is received in the detector 14, which includes the
sensors for measuring the amounts of radiation energy in the
absorption bands of water and keratin. The detector 14 eventually
supplies a signal RS which indicates the ratio between the amounts
of energy measured in the spectral bands of water and keratin.
FIG. 3 shows an electrical block diagram of the hair dryer. The
heating element 16 heats air which is blown past the heating
element 16 by means of a fan 18, which is driven by a motor 20. The
power of the heating element 16 and/or the speed of the motor 20
is/are controlled by a control unit 22 on the basis of the signal
RS from the detector 14. Thus, it is possible to reduce the power
of the heating element when the moistness of the hair decreases,
i.e. at a given value of the signal RS, in order to prevent the
hair from becoming too dry or from being scorched. Furthermore, the
control unit 22 communicates also with the light source 12 in order
to control and, if necessary, synchronize a chopper or another
modulation means.
FIG. 4 shows an implementation of the light source 12 and the
detector 14 in a simplified manner and not to scale. The light
source 12 comprises an infrared lamp 24 whose radiation energy is
focussed by means of a lens 28 so as to from a light beam 26. The
light beam 26 is periodically interrupted by means of a chopper 30.
The hair 10 reflects the light beam 26. A part of the reflected
light beam is received by the detector 14. The detector 14
comprises a lens 32, which focuses the received light beam onto a
diffraction grating 34, which provides the spectral separation of
the absorption bands to be measured. The sensors 36 and 38 are
arranged after the diffraction grating 34, one of the sensors, the
sensor 36, supplying a signal Ra which is a measure of the amount
of radiation energy in the absorption band around 1420 nm, and the
other sensor, the sensor 38, supplying a signal Rb which is a
measure of the amount of radiation energy in the absorption band
around 2058 nm. However, it is likewise possible to use more
sensors in order to analyze even more characteristic dips in the
received light beam. The signals Ra and Rb are amplified, filtered
and demodulated in respective signal processing circuits 40 and 42
and are applied to a signal divider 44, which divides the signals
Ra and Rb by one another and supplies the signal RS which is a
measure of the ratio Ra/Rb of the spectral energies in the measured
absorption bands. Amplification, filtering and demodulation are
customary techniques in the field of electronics. Dividing two
signals can be effected, for example, by means of a log/antilog
amplifier. Certain functions can also be performed in the digital
domain after the analog signals have been digitized by means of
analog-to-digital converters.
When the sensor 38, the signal processing circuit 40 and the signal
divider 44 are dispensed with, a system is obtained which is based
on an absolute measurement of the amount of energy in the
absorption band around 1420 nm.
* * * * *